1. Field of the Invention
The present invention relates to a method for controlling a hydraulic circuit for a twin-clutch transmission for motor vehicles, wherein the hydraulic circuit comprises a first and a second clutch that can be hydraulically actuated, the pressures of said clutches being controlled with respective pressure control valves, and wherein a safety circuit substantially guarantees a safe state for the hydraulic circuit if a malfunction occurs.
The present invention also relates to a hydraulic circuit for a twin-clutch transmission for motor vehicles, comprising a first and a second clutch that can be hydraulically actuated, having a first and a second clutch circuit, wherein the first clutch circuit comprises a first pressure control valve for controlling a first clutch pressure for the first clutch, and wherein the second clutch circuit comprises a second pressure control valve for controlling a second clutch pressure for the second clutch, and comprising a safety circuit which guarantees a safe state for the hydraulic circuit if a malfunction occurs.
2. Description of the Related Technology
Twin-clutch transmissions for motor vehicles have recently attracted particular interest. They are based on the basic concept of conventional manual transmissions but have two disengageable clutches. One disengageable clutch connects an engine output shaft to a first transmission branch which includes, for example, gear steps 1, 3, 5, etc. The second disengageable clutch connects the engine output shaft to a second parallel transmission branch which includes, for example, gear steps 2, 4, 6, etc.
The outputs (main drive pinions) of the two transmission branches are connected to a common output shaft which is connected to the driving wheels of the motor vehicle.
Overlapping actuation of the disengageable clutches enables overlapping gear changes of neighboring gear steps to be performed without interrupting the tractive force. This makes twin-clutch transmission very comfortable. Due to the fact that the transmission of force is performed in a frictionally engaged and/or positive-locking manner, comparably high efficiency can also be achieved.
Twin-clutch transmissions can generally only be operated automatically. Particular safety precautions must be taken in such cases to prevent two gear steps from being engaged simultaneously and loaded simultaneously via the disengageable clutches. This could result in the destruction of the wheel sets and/or the disengageable clutches. The disengageable clutches are generally hydraulically controlled clutches. The disengageable clutches can be constructed as dry clutches. It is, however, advantageous if the disengageable clutches are constructed as wet clutches, in particular as wet multiple-disk clutches.
The pressure control of the two disengageable clutches must be fast and, nevertheless, sensitive.
Some hydraulic circuits for the hydraulic control of a twin-clutch transmission comprise a first partial circuit for the first disengageable clutch and the first transmission branch as well as a second partial circuit for the second disengageable clutch and the second transmission branch.
The partial circuits are connected on the input side with a hydraulic supply respectively by means of release valves. The release valves are constructed in this case as “fail-safe” valves. In normal operation, the release valves are released electrically. When a failure of the electrical control occurs, the release valves are moved by springs to a disengaged position in which the partial circuits are disengaged from the hydraulic supply. At the same time, the hydraulic partial circuits are depressurized by connecting them with a tank. This disengages the two disengageable clutches. As a result, if such a malfunction occurs, the vehicle coasts and then comes to a halt.
Some embodiments have an emergency actuation device for an automated controllable clutch which is constructed so as to close passively. In this case, the emergency actuation device comprises a pressure accumulator as an auxiliary energy store for emergency actuation.
In some embodiments an arrangement comprising two check valves and a pressure limitation valve ensures that a pressure acting on the clutches does not exceed a maximum value.
Some embodiments have a hydraulic circuit for an automatic transmission. Instead of a hydrodynamic converter, the automatic transmission comprises a transmission clutch and/or a brake as a starting device.
To enable emergency operation even if the vehicle comes to a stop, it is provided that, if a malfunction occurs, the automatic transmission is controlled with a signal dependent on the vehicle speed and/or the engine speed. This enables the traction from the drive to the engine to be interrupted in a timely manner in order not to “stall” the engine in emergency operation.